The invention relates to electrically nonconducting hollow-profile structures, especially for SF.sub.6 insulated apparatuses and installations in high-tension and extra-high-tension ranges wherein the structure includes a glass-containing insulative component such as a glass reinforced plastic (GRP) core, and to whose ends attaching elements are fastened, and also to a method for protecting the glass-containing insulative component from the products of separation of the SF.sub.6 gas.
SF.sub.6 insulating gas is employed for insulation in high-tension (high voltage) and extra-high-tension applications such as in bushings for high voltage transformers operating in the 125 KV, 500 KV or higher voltage ranges. The use of electrically-insulating structural parts made of layered molded plastics built up out of plastic-impregnated polyester fibers for protection against agressive products of separation of the SF.sub.6 insulation gas, which attach glass, is already known.
In this connection, one disadvantage consists of the fact that in layered molded plastics of this sort, built up without any glass component, the polyester fibers have less interlaminar resistance to flexing, a lower E modulus, a lower thermal carrying capacity and generally worse mechanical characteristics than do the glass fibers. Therefore, it has already been suggested that such electrically non-conducting, hollow-profile structural parts as consist of a stress-receiving GRP core and a fiber/GRP/fiber/fiber casing or envelope be produced by a sandwich or layer construction method.
This latter arrangement has the disadvantage that the glass fiber interfaces of the GRP layered molded plastic come into contact, on the front sides of the profile structural part, with the formations of gas resulting from carona discharges in the SF.sub.6 insulation gas (i.e. products of separation of the SF.sub.6 gas), in which hydrogen fluoride (HF), with moisture (condensate) which possibly may be present, can change into hydrofluoric acid, which attacks the glass components and causes quartz to be released.
Another important disadvantage is to be found in the fact that glass fiber interfaces are exposed by the threading process on the surface of the ends of the profile structural part when there is a threaded or "screw" connection between the profile structural part and the attachment fitting. These exposed glass fiber interfaces can come into contact with the glass-disintegrating products of separation of the SF.sub.6 insulation gas.
In order to protect the glass fibers against products of separation of the SF.sub.6 insulation gas, it has been suggested that the exposed glass fiber interfaces be coated with a layer of lacquer or varnish. However, a relatively thin layer of such materials does not give the required protection, for the SF.sub.6 insulation gas products of separation can reach the GRP core of the profile structural part by diffusion and attack the glass component, destroying the insulating structural part in that way.